Branded, free-to-use antivirus products for Mac OS X are almost unheard of and the examples that do exist are designed to tempt users into upgrading to get more features and support or lack some features.

Sophos Anti-Virus Home Edition for Mac looks like becoming the first ever full-featured Mac security software with no designs on the wallets of ordinary users.

What users are being offered doesn’t appear to lack any of the features that would come with the plethora of paid-for Mac security products on the market. It scans files on demand, it sits in memory and monitors main memory for Trojan and virus attacks and exploits, and it will clean up infections it finds on compromised machines.

Users will also get indefinite signature file updates as new Mac malware is discovered, and will not be pestered to upgrade to a ‘full’ product because this is the full product.

What users don’t get is telephone support – they will be offered forum help instead - while business users requiring central management will continue to have to pay to license the software. There is no firewall or parental control settings. This is for anti-malware only.

So do Mac users really need antivirus software anyway, and what does Sophos get out of the deal for handing away free security?

“The Mac malware problem does exist. And unfortunately a lot of Mac users are very blasé about it,” said Graham Cluley of Sophos. “They are a soft target.”

The volume of attacks on Mac users is still tiny compared to Windows but there is evidence that in recent months the sophistication of their design has raised a notch or two. Only a week ago, the world got warning with a cross-platform attack based on Java. The attack was not serious but the intent is clear - Mac users are now in the sights of mainstream criminals.

In the past Mac users had favourable statistics in their favour, but going forward the simple equations of the past appear to be breaking down. This is exacerbated by the tendency of Mac users to leave their machines unprotected.

As to motivation, Sophos was looking for “brand awareness,” said Cluley bluntly. “It’s about getting our name out there.” The company will surely succeed in this ambition.

In Cluley’s view, with Anti-Virus Home Edition for Mac, Apple users have no need to pay for antivirus software. Rivals still charge significant annual sums for just such a thing so expect some of these companies to tear into Sophos in a bid to undermine it.

These companies face a tough fight to defend this position. Sophos is a significant business software company with a strong reputation. It will also continue to develop the product for paying business users.

The software is free to download from today for all Mac users running OSX 10.4 (Tiger), 10.5 (Leopard) or 10.6 (Snow Leopard) on Intel or PowerPC chips.

PC Tools also offers a free antivirus product for Macs called iAntivirus.